Journal Bearing Stribeck Explorer

What the app does

The Stribeck curve shows how the friction of a lubricated contact changes with speed, load and viscosity: high friction in boundary lubrication, a steep drop through mixed lubrication, a minimum at lift-off, and a slow rise again in full-film (hydrodynamic) lubrication. The Journal Bearing Stribeck Explorer computes this curve for a plain journal bearing from its geometry, load, oil and surface roughness, so you can see at a glance how far your operating point is from mixed lubrication.

The model follows the load-sharing concept of Johnson, Greenwood and Poon. The oil film is solved with the Reynolds equation on the finite-length bearing, with the Reynolds (Swift–Stieber) cavitation condition. Asperity contact is described with the Greenwood–Williamson model on the combined roughness of shaft and bushing. Film and asperities carry the load together on the same gap, and the app finds the eccentricity at which both together balance the applied load. Shaft and bushing are treated as rigid, the standard assumption of hydrodynamic bearing design.

The app is a quick estimate: no surface topography file is needed and a case is solved in a fraction of a second. For measured surfaces, spiral grooves and elastic deformation by FEA, use the Journal Bearing Simulator.

Inputs and outputs

1. Bearing geometry — journal diameter, bearing length and radial clearance.
2. Operating conditions — radial load, shaft speed and oil temperature.
3. Lubricant — from the built-in list or the i-TRIBOMAT tribology database, or a custom oil defined by its kinematic viscosity at 40 °C and 100 °C and its density.
4. Materials and surfaces — bushing material (bronze, steel, grey cast iron, aluminium alloy or white metal; the shaft is steel), the roughness Rq of shaft and bushing, and the boundary friction coefficient.

For each case (A, B, C) the app gives the eccentricity ratio, attitude angle, minimum film thickness, film parameter λ, the share of the load carried by the asperities, the friction coefficient and the power loss. Charts show the bearing cross-section, the pressure and film thickness around the bearing, and, on demand, the Stribeck curve: friction coefficient and asperity load share over shaft speed, for all active cases on the same axes.

Worked example

A plain bearing with a 50 mm journal, 40 mm length and 25 µm radial clearance, a bronze bushing, shaft roughness Rq 0.2 µm and bushing roughness Rq 0.6 µm, lubricated with an ISO VG 46 mineral oil at 60 °C, carrying 5 kN at 1000 rpm.

The app returns:

Quantity	Value
Eccentricity ratio ε	0.67
Attitude angle φ	45.7°
Minimum film thickness	8.3 µm
Film parameter λ	13
Load carried by asperities	0 %
Coefficient of friction	0.0034
Power loss	44 W

At 1000 rpm the bearing runs on a full oil film. The Stribeck curve shows the reserve: friction reaches its minimum of about 0.0012 near 180 rpm, asperity contact starts below about 150 rpm, and at 10 rpm the asperities carry most of the load and friction rises to about 0.10.

Typical uses

• Checking whether a plain bearing runs in full-film or mixed lubrication at its operating point.
• Finding the speed below which a bearing leaves full-film lubrication, for start-stop and low-speed operation.
• Comparing oils, clearances or surface finishes side by side for friction and power loss.
• Teaching the Stribeck curve and the lubrication regimes.

How to access the app

The Journal Bearing Stribeck Explorer runs in your web browser on Tribology Universe, the app platform of i-TRIBOMAT: The European Tribology Centre. Use is free; you only need a Tribology Universe account, which takes a minute to create.

References

• K. L. Johnson, J. A. Greenwood, S. Y. Poon, A simple theory of asperity contact in elastohydrodynamic lubrication, Wear 19 (1972) 91–108
• J. A. Greenwood, J. B. P. Williamson, Contact of nominally flat surfaces, Proceedings of the Royal Society A 295 (1966) 300–319
• A. A. Raimondi, J. Boyd, A solution for the finite journal bearing and its application to analysis and design: I, ASLE Transactions 1 (1958) 159–174
• O. Reynolds, On the theory of lubrication and its application to Mr. Beauchamp Tower’s experiments, Philosophical Transactions of the Royal Society of London 177 (1886) 157–234

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